6 Things You Probably Didn't Know About Your Muscles

There's not much we could do without our muscles -- swallow, breathe, move at all. Yet despite how essential muscles are to our survival, there's still a lot we don't know about them and how they work. Here are six fun facts you may not have known about your muscles.

There isn't just ONE strongest muscle in your body.

You've probably heard that your tongue is the strongest muscle, and while it is certainly impressive -- with its "combination of elasticity and forcefulness" -- LiveScience explains that there are too many different ways to measure strength to crown any one muscle strongest. The calf muscle, for example, is actually the muscle that exerts the most force, while the jaw muscle exerts the most pressure. And the gluteus maximus is the biggest muscle in the human body.

Muscles grow while you sleep.

All that work you put in at the gym pays off after you hit the hay. In the deep and restorative stages of sleep, the muscles relax and blood flow to the muscles increase. Hormones that fuel muscle development are released and tissues grow and repair, according to the National Sleep Foundation. Without enough deep sleep, don't expect to see results at the gym.

Muscles make 85 percent of your body heat.

When muscles contract, they give off heat -- enough of it to account for most of what keeps you warm and toasty, according to the National Cancer Institute. Muscles are also at work when we shiver: When the skin receptors send "brr" signals, the brain triggers some rapid-fire, involuntary muscle contractions -- those shivers -- to heat things back up.

It's easier to gain muscle than lose it.

Fall of the wagon, and you'll probably only lose half your bulk. That's because it seems to take twice as long to lose new muscle as it does to build it. One study found that new exercisers gained 47 percent more strength in two months of weight training. Then, after two months of taking it easy, they only lost 23 percent of that strength, Fitness magazine reported.

Muscle burns more calories than fat.

Your resting metabolic rate -- the number of calories you burn each day without doing a dang thing -- is intricately linked with your body composition. Muscle is more "metabolically active" than fat, meaning it naturally burns more calories when you're at rest. However, it's not enough to make the pounds just melt away. One pound of muscle at rest only burns six calories in an entire day, compared to the two calories a day burned by a pound of fat, the LA Times reported.

Muscle tissue makes up 35 to 40 percent of your body weight.

There are three types of muscle tissue -- skeletal, cardiac and smooth, and about 650 layers of skeletal muscle in the body.